Vegetation composition of extensive green roofs in Oslo, Norway
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Original versionBakhtina, M. Vegetation composition of extensive green roofs in Oslo, Norway. Master Thesis, University College of Southeast Norway, 2016.
Green roofs are systems which can be considered dynamic and living and at the same time engineered constructed system. In this thesis, I am looking at a specific type of green roofs – extensive green roofs with sedum-moss vegetation, which has a shallow depth of growing medium. The major objective of this thesis is to study extensive green roofs in the Oslo region to discover how their vegetation composition has changed after installation and to relate the vegetation composition to environmental conditions. Vegetation analyses were conducted and soil samples were taken on 18 extensive green roofs which were one to 13 years old. In addition, information about composition of the originally planted species, for each studied extensive green roof was obtained to compare with the current vegetation composition and richness. The results demonstrate that richness of the originally planted species has declined after the extensive green roofs’ installation. However, the richness of plant species has increased, because of spontaneously established species that were found. Half of the studied plots experience decrease of the originally planted vegetation. The results are discussed to find out the reasons behind the difference and changes of the vegetation composition on the green roofs. Abundance and richness of species are mostly affected by a biotic factor, such as the type of Sedum mix, abiotic factors, such as soil depth, pH, phosphorus, potassium levels, organic matter, and age. The conclusions are drawn for various factors that affect vegetation on the green roofs. Deeper and more acidic soils with a higher amount of organic matter support more spontaneously established species. Decline in abundance of originally planted species is associated with decline of pH level in the soil on extensive green roofs, shallow soil depth, and succession dynamics.